I have a 1999 Tahoe with 5.7 lilter engine.Service Engine Light came on,check it with OBD 11 scanner, code read P0304 (cylinder number 4 misfire).First thing did was change plugs and plug wires.code still came on.Used Bosh plugs and Autolight plug wires.Next thing did was replace the coil and idle air control valve.Code still came on and still idle rough.Though about mabe the #4 injector is bad.Will someone please help,tell me what u think i should,Thank U!!!!

 

Probably should have stuck w/ AC Delco plugs and wires.

 

X2 I have seen this problem before. They really like a/c plugs and wires. if you pull plug 4 you should be able to test for spark or see if there is to much gas or no gas.

 

Bosch plugs are junk unless they are in a German car. Most likely that is not the cause though since the code never changed. By process of elimination it must be the injector. There is a big problem with the poppet style injectors on these trucks. Switch all of them to they new style and you should be OK.

 

I have a 1999 Suburban with the 5.7 L 350 cid that I have been having cylinder 5 misfire for a while now. It would come in when I was going up a steep hill on the gas hard or when towing hard as well. I tried plugs, wires, cap, rotor and it would come back. Just this past week it started running a rough idle around town sitting at a light. I couldn't take it anymore so I just took it in this weekend to the shop so they could put in on the scope. I told them that I had changed everything and they insisted on new plugs but did see something occasionally on cyl 5 as well as a bit weak on cyl. 1 and 3. Notice all odd cylinders. The way I understand it is that there are not individual injectors but some sort of "Spider" something on each side. The code was cleared yesteday (2/26) and this morning sitting in a drive thru the check engine light came on and a small rough idle. The guy in the shop told me the unit for the one side would run about $1000 so that's why he wanted to start with plugs. I will call him tomorrow and let him know that the light came on. Don't know if I want to spend the 1000 but can't afford a new $60,000 truck .
This is just why I came on this forum, to see what everyone else is saying and what the cheap fix is.
Thanks
BTW- New to this forum stuff.